1. Field of the Invention
This invention relates to the cutting of vegetation, and more particularly, it relates to the cutting of vegetation using a flexible, non-metallic cutting line extending from a rotating head into a cutting plane.
2. Description of Prior Art
Various types of devices have been proposed for many years to facilitate the removal of vegetation by mowing, trimming, edging and like cutting operations. In general, these devices have employed a metal blade to effect vegetation removal. Devices of this nature employ prime movers such as electric and gasoline motors. As a result, rotating metal blades can inflict serious and terrible injury upon the user.
In the United States of America, practical vegetation cutting devices using flexible, non-metallic lines carried upon a rotating head were developed. Examples of devices are shown in U.S. Pat. Nos. 3,708,967, 3,826,068, 4,052,789, 4,054,992, 4,067,108 and 4,104,797. These patented devices have met outstanding success in that these American developments provide safer electrical or gasoline-powered tools for vegetation cutting, edging and trimming operations.
The devices shown in these patents employ a flexible cutting line, such as manufactured from Nylon.RTM. polymer. The cutting line is carried usually upon a spool internally of a rotating head. When desired to replenish the line or to extend an additional length of it, the rotation of the head was stopped and line manually extended from the spool. This line extension procedure in the patented devices has been found to be convenient, simple and reliable. In many of the more powerful devices, especially those powered by DC electric motors, a system to extend the cutting line from the head without interrupting cutting operations was desired.
A most desirable system would be capable of feeding cutting line as needed from the head so that line feeding is independent of operator action during grass cutting. Structures directed toward this purpose are shown in U.S. Pat. Nos. 3,895,440, 4,020,550 and 4,035,915. These structures have in common a basket-weave supply of cutting line carried on the periphery of a disc with the line feeding from behind special post members. These post members have a cutting-abrading edge so that cutting line from the weave supply is bent about such edge in the free traveling end portion extending into the cutting plane. The combination function of the edge, line, angular speed, etc., is arranged so that the line posts with such edge sever the free end of the cutting line when it is worn to an ineffective length. In practice, these structures are found to waste about 25 percent of the cutting line because of the excessive length of line severed at the post's edge, e.g., three inches.
Other line feeding structures are shown in U.S. Pat. Nos. 4,118,864 and 4,138,810. These mechanisms control spool rotation in line feeding functions by worm and spur gears having complex action in the vegetation cutting environment. Another line feeding mechanism is shown in U.S. Pat. No. 4,104,796 wherein speed sensitive cams control rotation of a spool within a cutting head.
Automatic cutting line feeding mechanisms have a common problem as to delay in feeding, overfeeding and excessive repeating or "machine gun feeding". This problem is particularly agrevating when the mechanism initiates and completes the cutting line extension cycle by sensing two set point conditions. For example, cams whose movement reflects one set point at a first rotary head speed and a second set point at a second rotary head speed tend to hunt, repeat and other malfunctions.
The present invention provides a rotating head with a simple mechanism that maintains the cutting line at its maximum preset length in the cutting plane irrespective of rates of cutting line wear or loss and without interrupting vegetation cutting or requiring independent operator action. The mechanism senses only one condition, e.g. speed of the rotating head to initiate the cutting line extension. However, the mechanism is self completing during cutting line extension.